Radiocecology
Page 148
the water was
manganese < iron < cobalt < zinc.
seep
me mepameten Be FRAR hatSS" Sh
The order of accumulation is therefore in agreement
with the order of stability of the metal-biological
sustrate complex and suggests that the primary process of accumulation of the radioisotopes of these
elements by plankton is probably that of surface
adsorption although the process of direct uptake
and assimilation may also occur.
In higher animals,
at least, these elements are intimately associated
with oxygen transport, electron transport, enzyme
function, and the structure of vitamin Bj9.
Although surface adsorption may be an impor-
tant mechanism in the uptake of radionuclides by
plankton, this process is of minor importance in
the accumulation of radionuclides by omnivorous
and carnivorous marine fishes.
In the fishes the
radionuclides considered here are primarily accumu-
lated by metabolic processes and the route of uptake is mainly through the food supply. Only those
radionuclides which are biologically important and
are subjected to only limited isotope dilution in
the sea are concentrated by the fishes. The radioisotopes of cobalt were concentrated more than the
other radionuclides by the plankton and contributed
43 per cent of the total radioactivity.
In the omnivorous fish
radioactive cobalt was discriminated
Whereas radioactive zinc contributed only 3 per cent
of the total radioactivity in the plankton it
accounted for about 59 per cent in the white muscle
and 10 per cent in the liver of the omnivore.
for metabolism in these active fish.
Radioactive manganese was not detected in the
plankton or omnivorous fish. In the tuna samples
manganese-54 accounted for up to 0.4 per cent of
the total radioactivity with an average percentage
in all organs approximately equal to the percentage of total radioactivity in the water contributed by that radicelement.
SUMMARY
Three factors appeared to control the seiective uptake of radionuclides from sea water by the
plankton, omnivorous fish, and carnivorous fish
studied. These were isotope dilution by the corresponding stable element or chemically similar
elment in the sea water, the tendency of divalent
cations to complex strongly with biological substrates, and the biological requirements for cer-
against, probably as a result of limited biological
demand, and accounted for only 10 per cent of the
total radioactivity in white muscle and 8.7 per
cent in the liver. In the tunas the percentages of
radioactivity contributed by the radioisotopes of
els were as follows:
ther to values of 0.9 per cent to 2.5 per cent in
the liver. Thus, the percentage of radioactive co-
During the first 48 hours following fallout
the plankton in the contaminated area accumulated
cobalt in the tissues and organs were reduced fur-
balt in the tissues and organs decreased progressively through the two higher trophic levels of the
food chain. This decrease may be attributed, in
part, to higher turnover rates for cobalt in marine
fishes than for iron, zinc, and manganese.
The elements iron, zinc, and manganese are
biologically important in enzyme systems and in
oxygen and electron transfer.
of hemoglobin, myoglobin,
Iron is a component
cytochromes, and cyto-
chrome oxidases and other enzymes associated with
oxidation.
Zinc is found in the respiratory pro-
tein of the blood in some snails and in the enzyme
carbonic anhydrase.
Manganese is associated with
peptidases, transphorases, dehydrogenases, decar-
boxylases, and oxygen disposal system in plants
(Eyster et al., 1958; Steward and Pollard, 1957).
tain elements in metabolic processes.
The uptake patterns in the three trophic lev-
radionuclides
they occurred
radioisotopes
and zinc were
comparison to
in approximately the same ratio as
in sea water. After one week the
of the three elements cobalt, iron
actively taken up by the plankton in
the other radionuclides which were
associated with the plankton at percentages similar
to those in sea water. Omnivorous fish which feed
on the plankton, almost completely excluded the
fission products and, on a comparative basis, concentrated zinc-65 and iron 55,59, but discriminated against cobalt-57,58,60. Carnivorous tunas,
which feed primarily on omnivorous fishes, discrim-
inated in favor of zinc and manganese and against
iron and cobalt in comparison to the relative per-
centages of these radionuclides in their food
supply.
Of the three elements, the radioisotopes of
iron and zinc were concentrated in the liver of
SPN i yay
In
the tunas the percentages were greater than those in
the flying fish, accounting for approximately 90
per cent and 78 per cent respectively in the muscle and liver of these carnivorous fishes. The
high levels of zinc-65 in the tissues of the tunas.
are probably related to the biological requirements
the omnivorous fish to a level in which the disintegration rate per unit weight of tissue was
approximately double that in the piankton. On a
percentage basis radioactive iron contributed 16
ACKNOWLEDGMENTS
This work was performed under contract number
AT(45-1)540 between the U. 8, Atomic Energy Commission and the University of Washington.
per cent of the total activity inthe plankton and
approximately 31 per cent and 81 per cent respectively in the white muscle and liver of the omniv-
orous flying fish. In the carnivorous tunas iron95,59 accounted only for an average of 7 per cent
and 20 per cent respectively in the same organs.
Thus the percentage of total radioactivity contrib-
uted by iron-55,59 in plankton was about
and 1/5
‘respectively of the percentage accounted for in
the white muscle and liver of the omnivore and
radioactive iron contributed only 1/4 as much of
the total percentage or radioactivity in the muscle
and liver of the carnivorous tunas as it did in the
corresponding tissues of the omnivore.
The reduction in percentage composition of
comtoeneg ive iron in the tissues of the
tunas
pared
w
those in the flying
fish is compensated
by the tncreased percentages of zinc-65
.—
REFERENCES
Anonymous.
1958.
The results of a physical and biological oceanographic survey at Eniwetok.
Staff,
Pacific Oceanic Fishery Investigations, U. S. Fish
and Wildlife Service, Honolulu, T.H.
55 pp.
Bonhan, K.
1958.
Radioactivity of invertebrates and
other organisms at Eniwetok Atoll during 1954-55.
Univ. of Washington, U. S. AEC report UWFL-53.
52 pp.
Donaldson, L.R., A.H. Seymour, E.E. Held, N.O. Hines,
F.G. Lowman, P.R. Olson, and A.D. Welander.
1956.
Survey of the radioactivity in the sea near Bikini
and Eniwetok Atolis, Univ. of Washington, U. 5S.
AEC report UWFL-46.
38 pp.
Eyster, C., T.E. Brown, H.A. Tanner, and 8.L. Hood.
1958.
Manganese requirement with respect to
growth, Hill reaction, and photosynthesig.
Plant
Physiol. 33: 235-241.